A teen straphanger was slashed in the face on an Upper East Side platform — ran covered in blood into Bloomingdale’s for help, police said.

Cops said the 16-year-old boy was attacked on the R train platform at 59th and Lexington at around 7 p.m. Wednesday night.

The bleeding teen rushed into the nearby luxury department store for help and store workers called 911.

He was stitched up at Columbia Presbyterian Hospital.

Police are investigating whether the attacker was trying to swipe the boy’s phone and believe the two may have known each other.

Cops said the victim is not cooperating with them.